Section 60 of the Federal Civil Service Act lists the basic duties of a German civil servant. It begins with one sentence. Beamtinnen und Beamte dienen dem ganzen Volk, nicht einer Partei. Civil servants serve the whole people, not a party. The next sentence explains what this means. Sie haben ihre Aufgaben unparteiisch und gerecht zu erfüllen und ihr Amt zum Wohl der Allgemeinheit zu führen. They must carry out their tasks impartially and fairly, and they must conduct their office for the good of the general public.
The idea is older than the Federal Republic. Article 130 of the Weimar Constitution of 1919 said: Die Beamten sind Diener der Gesamtheit, nicht einer Partei. Civil servants are servants of the whole, not of a party.